The present invention relates to the manufacture of melt-spun filaments and, in particular, to a reduction in amplitude of vibration of spun filaments passing through quenching and finish application zones, and a reduction in haul-off tension.
The manufacture of melt-spun filaments is typically achieved by extruding a molten polymer, such as polyester, polyamide, etc., through a spinneret and then cooling the filaments thus formed. Therebelow, the filaments are converged and gathered at a guide and delivered to a bobbin or further treatment station.
Cooling of the filaments is traditionally accomplished in a quench zone by blowing a stream of cool gas such as air across the filaments emerging from the spinneret, as demonstrated for example in U.S. Pat. Nos. 3,067,459; 3,070,839; 3,135,811; 3,259,681; 3,858,386; and 3,969,462. The air may be directed radially outwardly from within a circular array of filaments, i.e., so-called outflow quench.
It is also common to apply a finishing liquid to the filaments below the quench zone to lubricate and impart antistatic properties to the filaments. Application of the finishing liquid may be performed by passing the filaments over a convergence guide, e.g., a so-called skid guide in which the filaments are bundled together in mutually contacting relationship while the finishing liquid is flowed or sprayed onto the bundle of filaments, as described for instance in U.S. Pat. Nos. 1,943,353; 2,373,078; 3,041,663; 3,067,459; and 3,988,086.
The degree of molecular orientation of the filaments, (i.e., birefringence), produced by the abovedescribed melt-spun techniques is influenced by a number of factors, which affect the amount of tension to which the filaments are subjected upon emergence from the spinneret, especially the intensity of cooling and finish application imparted to the filaments. Although acceptable levels of birefringence can be achieved by current techniques, it is often difficult to impart these qualities uniformly. The present inventors have recognized that one factor contributing to this problem involves a tendency of the filaments to oscillate while passing through the quench and finishing zones. It will be appreciated that in an outflow quench environment, an oscillating filament will contact the quench air flow at various upstream and downstream locations within the flow and will thus be subjected to different quench air velocities (i.e., the quench air velocity gradually decreases in the direction of air flow). Accordingly, the filaments may be quenched at varying and unequal rates. In addition, the oscillating filaments may collide before being sufficiently cooled, thereby tending to coalesce.
Although the presence of a skid guide at which the filaments are bundled may result in a slight reduction in the amplitude of vibration, as compared with the absence of such a skid quide, the problem of non-uniform quenching and finish application is far from alleviated.
Another problem encountered in filament spinning operations involves the tendency for breakage or damage to occur due to the high amounts of tension to which the filaments may be subjected. One cause of such high tension is air drag which results from the tendency of the rapidly-traveling filament group to induce a substantial air flow. Besides being more susceptible to damage, the highly tensioned filaments require that greater amounts of energy be expended for maintaining the filaments at the required travel speeds.